The enstatite-diopside solvus in the system Mg2Si2O6-CaMgSi2O6 has been experimentally determined within the pressure range 5–40 kbars and the temperature range 900–1500°C. Experiments involving reversal of the phase boundaries by unmixing from glass starting material and by reaction of pure clinoenstatite and diopside showed difficulty in achieving equilibration due to persistence of metastable, subcalcic clinopyroxene and to the sluggishness of reaction rate. The experimental data showed that the temperature dependence of the diopside limb is less than previously accepted. At 1500°C and 30 kbars subcalcic diopside found by Davis and Boyd (1966) is shown to be metastable with respect to enstatite and more calcic diopside of composition En42.3Di57.7. The solvus widens with increasing pressure between 5 and 40 kbars at 1200°C, but at 900°C the pressure effect on the solvus is very small. The stability relationships of the four pyroxenes, protoenstatite, enstatite, iron-free pigeonite and diopside are summarized, based on data from the literature and the present study. 相似文献
Summary Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Toolangi during two ten year periods (1924–1933 and 1949–1958) have been analysed to determine their solar and luni-solar diurnal components. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. It is shown that there are marked differences in the dependence ofS andL on the various parameters and a tentative explanation of this phenomenon is given. 相似文献
A model metasomatized lherzolite composition contains phlogopite and pargasite, together with olivine, orthopyroxene, clinopyroxene and spinel or garnet as subsolidus phases to 3 GPa. Previous works established that at ≥1.5 GPa, phlogopite is stable above the dehydration solidus, determined by the melting behaviour of pargasite and coexisting phases. At 2.8 GPa, melts with residual phlogopite+garnet lherzolite mineralogy at 1195 °C and with garnet lherzolite mineralogy at 1250 °C are both olivine nephelinite with K/Na (atomic)=0.51 and K/Na=0.65, respectively. Recent work shows that melting along the dehydration (fluid-absent) solidus of the phlogopite+pargasite lherzolite at pressures <1.5 GPa is very different with the presence of phlogopite, decreasing the solidus below that of pargasite lherzolite. At 1.0 GPa, both phlogopite and pargasite disappear at temperatures at or slightly above the solidus. The compositions of two melts at 1.0 GPa, 1075 °C (with different water contents), in equilibrium with residual spinel lherzolite mineralogy are silica-saturated trachyandesite (5% melt fraction, 3% H2O) to silica-oversaturated basaltic andesite (8% melt fraction, 4.5% H2O). Both compositions may be classified as ‘shoshonites’ on the basis of normative compositions, silica-saturation, and K/Na ratio. Decompression melting of metasomatized lithospheric lherzolite with minor phlogopite and pargasite may produce primary ‘shoshonitic’ magmas by dehydration melting at 1 GPa, 1050–1150 °C. Such magmas may be parental to Proterozoic batholithic syenites occurring in Brazil. 相似文献
Adaptive practices are taking place in a range of sectors and regions in Australia in response to existing climate impacts, and in anticipation of future unavoidable impacts. For a rich economy such as Australia’s, the majority of human systems have considerable adaptive capacity. However, the impacts on human systems at the intra-nation level are not homogenous due to their differing levels of exposure, sensitivity and capacity to adapt to climate change. Despite past resilience to changing climates, many Indigenous communities located in remote areas are currently identified as highly vulnerable to climate impacts due to their high level of exposure and sensitivity, but low capacity to adapt. In particular, communities located on low-lying islands have particular vulnerability to sea level rise and increasingly intense storm surges caused by more extreme weather. Several Torres Strait Island community leaders have been increasingly concerned about these issues, and the ongoing risks to these communities’ health and well-being posed by direct and indirect climate impacts. A government agency is beginning to develop short-term and long-term adaptation plans for the region. This work, however, is being developed without adequate scientific assessment of likely ‘climate changed futures.’ This is because the role that anthropogenic climate change has played, or will play, on extreme weather events for this region is not currently clear. This paper draws together regional climate data to enable a more accurate assessment of the islands’ exposure to climate impacts. Understanding the level of exposure and uncertainty around specific impacts is vital to gauge the nature of these islands’ vulnerability, in so doing, to inform decisions about how best to develop anticipatory adaptation strategies over various time horizons, and to address islanders’ concerns about the likely resilience and viability of their communities in the longer term. 相似文献
A set of thermodynamic models is presented that, for the first time, allows partial melting equilibria to be calculated for metabasic rocks. The models consist of new activity–composition relations combined with end‐member thermodynamic properties from the Holland & Powell dataset, version 6. They allow for forward modelling in the system NaO–CaO–KO–FeO–MgO–AlO–SiO–HO–TiO–FeO. In particular, new activity–composition relations are presented for silicate melt of broadly trondhjemitic–tonalitic composition, and for augitic clinopyroxene with Si–Al mixing on the tetrahedral sites, while existing activity–composition relations for hornblende are extended to include KO and TiO. Calibration of the activity–composition relations was carried out with the aim of reproducing major experimental phase‐in/phase‐out boundaries that define the amphibolite–granulite transition, across a range of bulk compositions, at ≤13 kbar. 相似文献
Mower County is in southeastern Minnesota in an area underlain by sedimentary bedrock. These rocks are karsted Middle Devonian and Middle Ordovician limestone and dolomite. The karst features of the county were inventoried. These features include sinkholes, disappearing streams, caves, dry valleys, and springs. Previous karst mapping efforts for other counties in Minnesota have produced sinkhole probability maps and a springshed map. In Mower County, we have developed a new type of karst map using a geographic information system (GIS) to produce a karst unit map. Karst units are discrete three-dimensional bodies in which solution of the bedrock has resulted in the integration of surface water and groundwater. The field mapping and hydrologic investigations were done with conventional methods. The karst unit delineation was done using GIS technology, which allowed us to examine the county's karst using two-dimensional and three-dimensional views. Many different overlays of the karst elements were combined to better understand the landscape dynamics. Ultimately, it was the overlay of the karst features, hydrologic information, and depth-to-bedrock mapping on a shaded relief landscape morphology map which allowed us to best delineate the individual karst units. 相似文献
The distribution of iron and magnesium between coexisting garnet and clinopyroxene is expressed by the distribution coefficient KDga-cpx. This coefficient has been experimentally determined as a function of temperature and pressure, and is used to determine the temperature of equilibration of natural eclogites.
The presence of relict zoning in both garnet and clinopyroxene in low to medium temperature eclogites permits evaluation of the P,T path followed by these rocks during prograde metamorphism.
The average P,T path for eclogites of blueschist terranes (type C eclogites) is suggested to be 40°C/Kb during prograde metamorphism. The Tasmanian eclogite (type B) records crystallization along a different P,T path (lower pressure at given temperature) from those of the type C eclogites. Eclogites from the migmatite-gneiss terrances of Poland and Norway do not preserve evidence of prograde metamorphism in mineral zoning but indicate higher temperatures at the metamorphic maximum; pressures were similar to those attained by type C eclogites. 相似文献